Changes in Blood DNA CpG Methylation Levels in Response to Methadone Maintenance Treatment: Epigenome-Wide Longitudinal Study

Background/Objectives: Methadone maintenance treatment (MMT) is one of the major pharmacotherapies for opioid use disorder. The underlying mechanisms of addiction and the treatment response are only partially understood. The study’s main goal was to identify differential DNA CpG methylation that occurred in response to MMT. Methods: Toward this goal, we have conducted a longitudinal epigenome-wide study of blood samples from 64 patients at the beginning and after 1–3 years of MMT, using a linear mixed model. Results: A total of 1881 differentially methylated probes (DMPs) were identified (FDR < 0.05), controlling for sex, age, estimates of blood cell proportions, and the first two principal components based on genome-wide SNP genotypes. Among the genes annotated to the top DMPs are DGLUCY, NXNL2, SOX10, and NPAS3. Several genes associated with substance use disorder were annotated by the identified DMPs, including ADORA2A, BDNF, CACNA1D, CREB1, CRHR1, CRY1, DNMT3B, GABRD, GNAS, GRIP1, OXR1, PRKACB, SCN2A, and SCN3A. The most overrepresented pathway is the small GTPase-mediated signal transduction pathway, and the most overrepresented process is the actin cytoskeleton organization. Conclusions: The study provides preliminary insight into the epigenetic effect of MMT. Future studies will have to confirm the DMPs, assess their impact on gene expression, and determine their clinical relevance.